Abstract
Detailed investigations of Ni substituted Fe0.994Ni0.007Te0.66Se0.34 and unsubstituted Fe0.99Te0.66Se0.34 crystals were performed at ambient pressure and under hydrostatic pressure in order to understand the complex relationship between structure, magnetism, and superconductivity in iron selenides. The aim of the investigations was to determine the structural and superconducting state properties and study their evolution under pressure, up to 11 kbar. A comparison of Fe0.99Te0.66Se0.34, a material with much less developed phase separation, with FeTe0.5Se0.5, a material exhibiting pronounced nanoscale phase separation, was also performed. Under ambient pressure, a weakening of superconducting state properties was observed in the Fe0.994Ni0.007Te0.66Se0.34 crystal, with disorder introduced by Ni substitution, as compared with those in Fe0.99Te0.66Se0.34. For Fe0.994Ni0.007Te0.66Se0.34, the x-ray diffraction studies have revealed a degradation of crystal quality under applied elevated pressure. Superconducting state properties of the single phase Fe0.99Te0.66Se0.34 crystal, such as upper and lower critical fields, were found to be poorer, at both ambient and hydrostatic pressure, than those observed for FeTe0.5Se0.5 crystals exhibiting pronounced nanoscale phase separation. Comprehensive studies of the impact of pressure on crystal structure and on superconducting state properties confirm that enhancement of superconductivity correlates with the appearance of mosaicity under pressure. The above observation leads to the expectation of a pressure-induced increase in inhomogeneity, leading to the enhancement of superconducting properties in other sulpho-iron seleno-tellurides of anti-PbO-type structure.
Highlights
Introduction anDiscovery of superconductivity in layered iron chalcogenides of general formula Fe(Se,Ch) (“11”-type compounds, where Ch = S, Te) has activated detailed studies of metal chalcogenides [1]
In order to better understand the possible connection between the crystal inhomogeneity and superconducting properties, we decided to investigate the
Type, the quality was insufficient for studies of structure details
Summary
Single crystals of nominal composition of FeTe0.65Se0.35 and Fe0.995Ni0.005Te0.65Se0.35. The thermal conditions of synthesis and crystal growth were as follows: the ingot was heated for 3 h at oC, the temperature was risen to 920 oC After melting, this temperature was kept for cri pt h, the samples were cooled down to 500 oC with a rate of 5 oC/h and next to 200 oC with a rate of 60 oC/h, and cooling down to room temperature with the furnace was performed [23]. The studied single pte crystal was glued to the culet surface of the first diamond anvil together with a small ruby chip and placed in a 0.3 mm diameter hole of a 0.1 mm thick tungsten gasket. The background signal coming from the pressure cell was subtracted basing on measurements performed under ambient pressure for the sample mounted (i) directly on the diffractometer stage and (ii) mounted inside the pressure cell
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